So-called pantograph doors for buses have long been known. In them, a hinge device is formed by a pair of arms whose one end respectively attaches at the level of a body-mounted axis and whose other end attaches at the level of an axis connected to the door. The effective length of these two arms, that is to say, the spacing distance between their two axes, must be equal, and so must also the spacing distance between the two door side axes be equal, on the one hand, and the spacing distance between the two body-mounted axes on the other hand, so that the door maintains its orientation upon opening and closing and so that, in an open position, the door can hang next to the door opening and be parallel to said opening against the body.
The parallel movement of the door leads to the situation that, upon closing, such doors are engaged all at once by the totality of their edges into the frame of the door opening, so that if another window or door is not open on the vehicle body, a temporary buildup of excess pressure is generated on the interior of the motor vehicle by the inward movement of the door, said pressure slowing down the movement of the door and, in this manner, hindering the door locking mechanism from catching. Another problem consists therein that when the door is inadvertently opened while the vehicle is being driven, the relative wind—as opposed to the conventional case in which a door is mounted to the body by a single hinge on the front door edge, relative to the direction of travel—can bear down behind the partially-opened door and pry it completely wide open.